Internet activists are up in arms after a law that many fear will curb the Philippines' freedom of expression on the Web took effect this week.

While the government insists the Cybercrime Prevention Act of 2012 is intended to criminalise identity theft, hacking, spamming, online trafficking, and file sharing, opponents are concerned about penalties for social network posts that might be deemed libellous.

The libel portion was a last-minute amendment to the bill, which was originally introduced in July 2011. According to the act, online libel "committed through a computer system or any other similar means which may be devices in the future" is prohibited, prompting concern that it might result in a chilling effect on the use of services like Facebook and Twitter in the region.

Filipinos who post comments that are deemed defamatory by local authorities will face up to 12 years in prison and a fine of 1 million pesos (£15,000), according to the AFP. Newspaper employees face separate prison terms of four years and fines of 6,000 pesos (£90).

The bill also lets authorities collect personal data from user accounts and listen to voice and video calls on services like Skype without a warrant, AFP reported.

The United Nations Human Rights Council has deemed the bill "draconian".

Already, five petitions have been filed with the Filipino Supreme Court, claiming the law is unconstitutional and dangerously vague.

"Virtually any person can now be charged with a crime – even if you just re-tweet or comment on an online update or blog pst," Senator Teofisto Guingona, the government's only opponent to the bill, said in his petition, according to the AFP. "The questioned provisions ... throw us back to the Dark Ages."

In August, Malaysian Web activists participated in an "Internet Blackout Day" in retaliation for a Parliament ruling that could send Internet users to court for posting defamatory comments on any website.

Earlier this year, many groups joined forces to go after the Stop Online Piracy Act (SOPA) and the PROTECT IP Act (PIPA) in the US. Thanks to a joint Internet blackout, both bills were tabled, but other threats exist, according to organisers, like the pending CISPA legislation as well as ACTA overseas. Groups like the Internet Defense League have since emerged to combat these threats.